<div *ngIf="messageService.messages.length">
    <h2>Messages</h2>
    <button class="clear" (click)="messageService.clear()">
        Clear Messages
    </button>
    <div *ngFor="let item of messageService.messages">
        {{ item }}
    </div>
</div>
<div *ngIf="!messageService.messages.length">
    <h2>Messages is null!</h2>
</div>